The athletes sported the close-fitting face masks covering their nose and mouth as they pushed their luggage through Beijing International Airport.

The city’s pollution and scorching heat have been a major cause for concern for athletes headed to the Games, which start today when the US women’s soccer team takes on Norway.

The Olympics officially open Friday, when 91,000 people will pack the National Stadium, or “Bird’s Nest,” for the opening ceremony.

Beijing has struggled to reduce the sooty blend of ozone, carbon monoxide, nitrogen dioxide and sulfur that frequently covers the city at a level five times higher than the World Health Organization’s safety standard.

The Chinese government has taken several radical steps to improve the atmosphere in time for the Summer Games, including curbing car use and closing down factories.

Arne Ljungqvist, the International Olympic Committee’s medical commission chief, downplayed the smog concerns, saying Beijing’s air quality does not pose any problems to athletes “unless they have a specific condition such as asthma.”

The masks worn by the cyclists were designed and issued by the US Olympic Committee, which recommended that athletes wear them in the Chinese capital.

But USOC officials were unhappy with the fashion statement and reprimanded the cyclists for walking off the plane with them on.

“This is really a surprise because I didn’t think it was going to be such a big deal,” said Mike Friedman, 25, a track cyclist. “Why we wore the masks is simple – pollution!”

The whole city was enveloped in a blanket of smog for a second straight day, just 72 hours before the opening ceremony.

And the smog was so bad that it was visible inside.

The National Aquatics Center – known as the Water Cube – was filled yesterday afternoon with haze, officials said.

Australian swimmers got a chance to test the waters inside the 17,000-seat venue – which will host the swimming and diving competitions – and noticed the layer of haze hovering inside the $200 million complex.

“I am trying to find the answer to that question,” Australia’s swim coach Alan Thompson said when asked to explain where the mist had come from. “I don’t know why, but I did notice the haze.”

The IOC has said that it would reschedule outdoor events that last more than an hour – such as the marathon – if the air quality was bad, but they have not addressed the possibility that indoor events could also be affected.

Most swimmers had expected to be largely sheltered from the smog, although the polluted pool problem was evidence that no athlete can run from the issue. With Post Wire Services